This invention relates, in general, to diffusion bonding and, more specifically, to compositions for bonding titanium alloys to either steel or to nickel alloys, such as nickel superalloys. In particular, the present invention relates to a three-layered metallic interlayer material comprised of a first layer comprising nickel, overcoated with a second layer comprising copper, further overcoated with a third layer comprising a Group V-B metal. The nickel layer is placed in contact with the steel or nickel alloy while the Group V-B metal layer is placed in contact with the titanium alloy.
In the gas turbine industry, hybrid metal and composite shafts have been constructed to withstand the torsional and bending stresses placed on a small diameter drive shaft for a turbine engine. Shafts, for example, comprising a thin-wall metal (e.g. steel) tube with integral splines on both ends and a filament (such as boron filament) reinforced metal matrix composite cylinder (e.g. titanium matrix) metallurgically bonded to the metal tube inner diameter have been produced. The fibers in the metal matrix composite run parallel to the axis of the shaft. The composite sleeve is fabricated and bonded to the inner diameter of the metal tube by winding the composite monolayer tape on a mandrel with the filaments axially aligned. The mandrel is then inserted into a metal outer tube. The assembly is encapsulated, evacuated, sealed and pressurized at a sufficient temperature to achieve consolidation and diffusion bonding of the wound composite to itself and the shaft inner diameter. This process results in a fully consolidated hybrid shaft having a metal outer shell and a metal matrix composite inner sleeve reinforced by filaments, such as those made of boron, to enhance bending stiffness.
While it is highly desireable to specifically use titanium matrix composites and steel or nickel alloys, titanium does not form high-strength metallurgical bonds with steel or nickel alloys. This is due to the formation of brittle iron-titanium or nickel-titanium intermetallic compounds and titanium carbide. These brittle constituents form at the interface of the two alloys and provide an easy fracture path.
It is, therefore, an object of this invention to provide high-strength metallurgical bonds between either iron or nickel alloys and titanium alloys.
It is another object of the present invention to provide metallurgical bonds between either iron or nickel alloys and titanium alloys without the formation of brittle iron-titanium or nickel-titanium intermetallic compounds and titanium carbide.
It is still another object of this invention to provide an interface material which provides progressive compatibility between iron or nickel and titanium alloys.
It is still a further object of this invention to provide improved combined metal and composite shafts used in a gas turbine engine.
It is yet another object of this invention to produce a composite shaft for a gas turbine engine having a steel outer sheath and an interior shell constructed of a titanium matrix composite containing axially aligned filaments of a high modulus material, said interior shell being completely consolidated and bonded on the inner diameter of the outer steel or nickel alloy sheath.
It is still another further object of the present invention to provide a composite shaft wherein there is progressive compatibility between an outer steel or nickel alloy sheath and a titanium matrix composite containing axially aligned filaments, diffusion bonded thereto.